To avoid any leftover Champagne, buy a split (187 milliliter) of Champagne for this recipe.
Cook sugar in a small saucepan over medium heat, tilting pan occasionally, 10 minutes or until caramel colored. Remove from heat, and gradually pour Champagne over sugar (mixture will bubble and seize). Let stand 5 minutes.
Cook mixture over medium-low heat, stirring occasionally, 15 minutes or until sugar is dissolved (mixture will be syrupy). Remove from heat, and let cool 30 minutes.
Combine grapefruit and orange sections in a bowl. Pour Champagne mixture over fruit. Cover and chill 2 to 24 hours. Garnish, if desired.
White Grape Winter Fruit Compote: Substitute white grape juice for Champagne. Proceed with recipe as directed.